1. Field of the Invention
The present invention relates to a method for recognizing a printed circuit board (PCB) fiducial mark, and more particularly to a method for recognizing a PCB fiducial mark in order to decide an origin point in a chip mounter so that electronic parts can be mounted on a desired position of the PCB.
2. Description of the Prior Art
An internal circuit is used for connecting a number of parts in order to attain an operation of a device which performs the operation. A PCB is comprised of several electronic components that are integrated on a small panel. The greatest distribution of the electronic components is manufactured by a printing method. Currently, printed circuit boards of a single pattern contain a high density of electronic components in order to reduce the size of both faces of the board. Because electronic machines tend to be popular, printed circuit boards with a single pattern have been manufactured in large quantities at one time.
PCB fiducial marks are used as a reference location for yielding location data of electronic components for inserting into the PCB by indicating marks such as a circle, a triangle, or a square and recognizing a location, a direction, and a distance of the PCB. Chip mounters recognize a fiducial mark indicated on a PCB, on which electronic parts such as a semiconductor, a resistor, and a capacitor are mounted, so a location, a direction, and a distance of the PCB can be determined.
In the PCB, there characteristically exist a plurality of candidate objects around the fiducial mark due to a circumstance and an illumination. If a same algorithm is applied to the plurality of candidate objects as that which is applied to real fiducial marks, in order to recognize the fiducial mark, the calculation amount is congested. Therefore, it is necessary to divide a real fiducial mark from plurality of candidate objects. The best method for dividing a real fiducial mark from other candidate objects is a method in which geometrical characteristics are used.
U.S. Pat. No. 5,138,667, (issued to Roger H. Rich, Vaclav VINOUS, and Caimans on Aug. 11, 1992) discloses one example of a PCB fiducial mark recognition method for deciding an origin point in a chip mounter. U.S. Pat. No. 5,138,667 is directed to a process and device for detecting print registration marks on a multi-color printing press processing sheet or web-shaped matter having an area for printing of accuracy control signs or marks. A process consists of detecting a print registration mark composed of recognition signals and of a color pilot mark, comparing the image of the signs of the printed registration mark to the signs of a virtual reference registration mark, then defining a basic area for each sign, calculating a geometric center of every basic area, detecting any color pilot mark in these basic areas, calculating and memorizing the geometric center for the detected pilot mark, measuring an offset position between the geometric center of the basic area and the geometric center of the detected color pilot mark and utilizing the measured offset position for controlling a misregistration correction appliance of a printing press. The device for accomplishing the process includes an arrangement for performing each of the above-mentioned steps.
U.S. Pat. No. 5,138,667 can correct lengthwise and crosswise print misregistration and which considerably enhances the reliability for scanning of the marks but cannot recognize a damaged object and cannot recognize a candidate object with respect to a same pattern fiducial mark regardless of a size.